Our most successful tree?

Callery pear (white flowers) in a detention basin, Pyrus calleryana

Reforest the Bluegrass is one of the oldest and most successful community forestry programs in the US. Every year in April, thousands of volunteers turn out to plant trees from the Kentucky Division of Forestry nursery. The purpose of the program is to establish forests along riparian zones to protect water quality. There is no question that this program has benefited Lexington, Kentucky, and it has spawned similar efforts throughout the state.

Over the last several years, I have been looking at older Reforest the Bluegrass sites around Fayette County. Last year, I was joined by students from the Natural Resource and Environmental Science program at the University of Kentucky. In the course of our surveys, we found that most species that are being planted during Reforest the Bluegrass events are doing well.

At some sites, though, there is one tree that is more successful than the others, and it is one that nobody plants. The tree is callery pear, Pyrus calleryana, better known by its cultivar names Bradford pear and Aristocrat pear. All the white-flowering trees in the picture above are callery pears established from seeds brought in by birds.

These ornamental pear trees (with inedible fruit) are very popular among developers, who have planted callery pear in nearly every new housing project in the city, until it was finally banned. Although no longer permitted as a street tree, there are still thousands in the city and they are readily available to homeowners at local nurseries and big box stores. Technically, these trees in this picture are neither Bradford nor Aristocrat pears, because those are cultivars that have to be grown from cuttings. These trees are the progeny of those cultivars that are genetically distinct from the parents.

The fruits are dispersed by birds, and the tree has become established throughout the region. The picture at the top of this page is just one example of the great success of this tree: every white-flowered tree in the picture is a callery pear.

Is this a problem? Well, probably not. There is no evidence that this tree is displacing more desirable native trees. It certainly is providing shade and soil stability to the riparian areas that we are trying to protect. As the native trees, both the ones planted in Reforest the Bluegrass and volunteers, get taller, they will eventually shade out the callery pears and they will die.

Callery pear is an important lesson in unintended consequences. The horticulture industry gave no thought at all to the invasiveness of the tree, and it was planted everywhere. It should come as no surprise that it is very successful in disturbed sites all over the Bluegrass.